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Permanent magnet synchronous motors (PMSM) are very popular in the industrial market. Recently, robots are installed to compensate for the shortage of labor. Due to the increase in motors, the number of power lines and position sensor cable wiring are increased; this increase in complicated wiring is a problem. As a method to solve these problems, power superimposition technology in the power line of a PMSM is expected to reduce the distribution cables. In this paper, the power superposition technology method, and circuit equations of mounting transformers in power lines are presented and are then verified by experiment, simulation, and linear analysis. The circuit equation is proposed as a three‐phase circuit equation, which is transformed into a dq‐circuit equation by a transformation matrix. The characteristics of the electric angular frequency versus the dq‐axis voltage demonstrated satisfactory results, with errors within 1% in linear analysis and simulation. The linear analysis and experiment are shown to be similar, although there are some errors. The validity of the circuit equations could be demonstrated by the verification results. [ABSTRACT FROM AUTHOR]

Silicone gel is widely used to encapsulate power modules, and improvement of its dielectric strength has been required. So, the purpose of our research is to improve dielectric strength of silicone gel encapsulant, and we focus on crosslinking degree of silicone gel. Previous studies have shown that growth mechanism of electrical tree changes with crosslinking degree of silicone gel. This suggests the possibility that the presence of the interface by different crosslinking degrees inhibits the tree growth. In this paper, we have investigated the tree growth and breakdown characteristics in silicone gel—crosslinking degrees graded layer materials. The interfaces in our study are arrange as being vertical to the line of electric force. Consequently, it was clarified that barrier effect of interface by different crosslinking degrees and the relaxation of electric field in low crosslinking degree region retards on tree growth, which improves the dielectric strength. [ABSTRACT FROM AUTHOR]

Accurately calculating the transmission‐line constants of underground cables is important for various types of power system simulations such as electromagnetic transient, power flow, and transient stability simulations. The transmission line constants of cables installed in a tunnel must be calculated taking the skin and proximity effects into account, since the cables are spaced closely to each other and also to a wall face of the tunnel. However, the conventional method, which is capable of considering the skin and proximity effects, has been restricted to circular cross‐section conductors such as cables and a circular tunnel. Therefore, the method cannot handle a tunnel with a rectangular cross section. In this paper, a method for calculating the transmission‐line constants of a conductor system in which both circular and rectangular cross‐section conductors present in the same space is proposed. Then, the walls of a rectangular tunnel are represented by eight rectangular conductors, and cables represented by circular conductors are placed inside the eight rectangular conductors. In this paper, the proposed method is verified by experiments using a conductor system in which three circular conductors are arranged in a rectangular conductor. Calculated results obtained by the proposed method agree well with the measured results. [ABSTRACT FROM AUTHOR]

Accurately calculating the transmission‐line constants of underground cables is important for various types of power system simulations such as electromagnetic transient, power flow, and transient stability simulations. The transmission line constants of cables installed in a tunnel must be calculated taking the skin and proximity effects into account, since the cables are spaced closely to each other and also to a wall face of the tunnel. However, the conventional method, which is capable of considering the skin and proximity effects, has been restricted to circular cross‐section conductors such as cables and a circular tunnel. Therefore, the method cannot handle a tunnel with a rectangular cross section. In this paper, a method for calculating the transmission‐line constants of a conductor system in which both circular and rectangular cross‐section conductors present in the same space is proposed. Then, the walls of a rectangular tunnel are represented by eight rectangular conductors, and cables represented by circular conductors are placed inside the eight rectangular conductors. In this paper, the proposed method is verified by experiments using a conductor system in which three circular conductors are arranged in a rectangular conductor. Calculated results obtained by the proposed method agree well with the measured results. [ABSTRACT FROM AUTHOR]

Accurately calculating the transmission-line constants of underground cables and gas insulated bus (GIB) is important for various types of power system simulations. When calculating the transmission-line constants of a three-phase enclosure-type GIB, the Cable Constants supporting routine of EMTP is usually used. However, this routine could cause numerical errors, since the proximity effect is ignored for the calculation of series impedances and shunt admittances. In this paper, a method for calculating the transmission-line constants of a three-phase enclosure-type GIB considering the proximity effect is proposed. Then, series impedances and shunt admittances are accurately calculated by the method of moments with a surface admittance operator (MoM-SO) and method of moments (MoM), respectively. In this paper, the proposed method is verified by experiments using the small-scale model of a three-phase enclosure-type GIB. Calculated results obtained by the proposed method agree well with the measured results. [ABSTRACT FROM AUTHOR]

Metal strands of composite fiber-optic ground wire (OPGW) are sometimes melted and broken by high-energy lightning strikes. Direct current (DC) arc tests simulating the lightning strikes have thus been performed to obtain the melting and breaking characteristics of OPGW strands. J-Power Transmission Network Co., Ltd. has developed high strength and high-corrosion-resistant OPGW for long-span 500 kV overhead transmission lines crossing straits. This paper describes the melting and breaking characteristics of the OPGW strands due to DC arc discharge simulating high-energy lightning strike. In this research, the tests were performed using two kinds of arc, one was the arc supposing summer lightning whose polarity was negative with a relatively short duration, and the other was the arc supposing winter lightning whose polarity was positive with a relatively long duration. Furthermore, the calculations regarding the melting and breaking of OPGWstrands were carried out, and the calculation results showed a tendency similar to the test results. [ABSTRACT FROM AUTHOR]

In this paper, a touch fault calculation method is proposed based on the symmetric coordinate method. The touch fault in this paper means that a line‐to‐line short circuit fault occurred on parallel transmission lines stringing on a same tower. It is known that the touch fault occurs very rarely such as the galloping phenomena, and it causes an abnormal voltage rise especially on a low‐voltage transmission line. However, a quantitative analysis method of the abnormal voltage has not been proposed. Therefore, a general analysis method of the voltage profile solution for the touch fault is proposed based on the symmetrical coordinate method. The proposed method is able to calculate the precise voltage and current profile solution efficiently by introducing the similar formation for the touch fault solution same as the general fault solution. Demonstrative result to the application in the touch fault calculation is presented in order to verify the practicability of the proposed method. [ABSTRACT FROM AUTHOR]

In this paper, the influence to electromagnetic environment was evaluated on the outside of buildings where power line communication (PLC) systems were installed to a three-wire three-phase power distribution line. The electric field strength was measured at 140 points in five factories, in two office buildings, and in one stadium. Since many radio waves existed in the environment, the electric field strength when PLC system was operated and was not operated was measured. The influencewas evaluated by the cumulated occurrence probability because the frequency characteristics of the electric filed strength changed by the measurement points. The results showed that the occurrence probabilitywas not changed when the PLC system was operated and was not operated. The electric field strength was calculated by the common mode current obtained from the test result, and this indicated that the occurrence probability was lower than the measured occurrence probability of electric field strength. [ABSTRACT FROM AUTHOR]

SUMMARY Constant power factor control of a power conditioning system in a large-scale photovoltaic generation system (PV system) such as a mega-solar system is introduced to mitigate voltage variations on a distribution line. However, it is difficult for the control to mitigate the voltage variation on a long distribution line because of the changes in the loss on the distribution line. This paper proposes an advanced reactive power control in which the power factor of the PV system is adjusted using both the output power of the PV system and the apparent power of loads not to minimize the voltage variation at the interconnecting point but to minimize the voltage variation over the whole distribution line. We report on the results based on numerical analysis on mitigating the voltage variation by applying this control. This paper shows that the proposed control can mitigate the voltage variation better than constant power factor control can. The proposed control has the potential to be used as a measure for suppressing voltage variations on a long distribution line. [ABSTRACT FROM AUTHOR]

This paper describes line loss minimization control using the shunt and series converters of a UPFC (unified power flow controller) in a loop distribution system. The line losses in a loop distribution system are caused by the circulating current flowing in the loop and the mesh currents flowing to the loads. The authors have previously proposed a compensation method for circulating current using a series converter. In this paper, the authors propose a suppression method for reactive currents using a shunt converter. In the prototype model of a loop distribution system, a theoretical loss reduction ratio of 92% without line loss caused by active currents is obtained. Similar line loss reduction characteristics are obtained in experiments using the prototype distribution system. [ABSTRACT FROM AUTHOR]

SUMMARY: Generally, if power transmission lines are heavily loaded, the transient stability and frequency stability tend to be worse, and one power system fault may cause wide‐area blackouts. However, restriction of the power flow sacrifices economical operations. To solve this problem, CEPCO (Chubu Electric Power Co., Inc.) has implemented the online stability control system. Since a current system was constructed more than 20 years ago, the situation of power system has drastically changed such as a large‐scale introduction of distributed energy resource or increase of cross‐regional power interchange. To cope with these changes, we are developing a new stability control system with new control functions. And, the new system integrates current systems which were constructed separately for the purposes. As the result, the number of equipment was dramatically reduced. This paper describes an outline of developing system and new stability control functions to overcome various situational changes that have happened in CEPCO power grid. [ABSTRACT FROM AUTHOR]

SUMMARY Electromagnetic transient (EMT) simulations of power systems require accurate representation of models in a wide range of frequencies. This of course applies to the representation of transmission lines, and the phase-domain frequency-dependent line model is often used to this end. The phase-domain line model does not require modal transformation in EMT simulations but requires modal decomposition at its model identification stage, and there are cases where it fails to fix switchovers of propagation modes with respect to frequency. Thus, a frequency-dependent line model which essentially avoids modal decomposition is desired. This paper studies the possibility of a frequency-dependent line model based on the FDTD (Finite Difference Time Domain) method as a candidate which satisfies the above-mentioned requirements. First, improvements regarding computational efficiency and numerical stability are made to Kordi's FDTD-based frequency-dependent line model. Then, the following points are clarified using the developed model: (i) Waveform deformations due to propagation modes with different velocities can be reproduced completely without modal decomposition; (ii) As the time step size becomes larger, waveforms obtained by the developed model become less accurate due to the embedded filter for numerical stability. These points assure, if the error due to the embedded filter is reduced, that the developed model can become a useful frequency-dependent line model without model identification problems. [ABSTRACT FROM AUTHOR]

SUMMARY The Fault Current Interrupting Arcing Horns (FCIAH) is a new type of arcing horns, which operates to break fault current within one cycle of alternating current and contributes to reducing the instantaneous power interruption due to the opening of a circuit breaker. However, reportedly the transmission line is often tripped by the line protection relay in some power utilities, even though the FCIAH successfully could break fault current. In this paper, we have investigated primary factors in the unwanted operation of the line protection relays at the current interruption by the FCIAH, and have proposed effective installation strategies of the FCIAH considering the operational coordination with the responses of the line protection relays. [ABSTRACT FROM AUTHOR]

Much of oil-filled (OF) cable has been used for a long time as 66- to 500-kV extrahigh-voltage cable. Sometimes we can see extremely degraded tan δ oil (several tens of percent of tan δ, for example) in joint boxes, etc. The values of tan δ calculated by a simple combination model of paper/oil show that the oil-impregnated paper with such a high tan δ oil likewise has an extremely high tan δ, which must result in thermal breakdown. However, such an event has not taken place up to the present in actually operated transmission lines. This fact suggests that some mechanism for the suppression of tan δ has acted in the paper insulation impregnated with degraded tan δ oil. Therefore, we investigated in detail the tan δ characteristics of paper impregnated with extremely high tan δ oil. In addition, based on the investigation results, we developed a method for simulation of heat generation by dielectric loss in an OF cable joint (which has degraded tan δ oil). © 2011 Wiley Periodicals, Inc. Electr Eng Jpn, 178(1): 1-10, 2012; Published online in Wiley Online Library (). DOI 10.1002/eej.21184 [ABSTRACT FROM AUTHOR]

This paper describes a method for calculation of the effective relative dielectric constant ℇs of VVF cable. For power line communications (PLC), VVF cables in homes are used as 2- to 30-MHz high-frequency transmission media. As they are not designed and installed for such transmission media, there are many branches and impedance mismatch points that cause PLC signal reflections and standing waves. In order to estimate such standing wave generation and estimate undesirable PLC signal radio wave leakage, the length of the cable and the relative dielectric constant ℇs are important. However, the insulator of VVF cable is thin and not symmetric, so that it is not easy to calculate effective ℇs analytically. In this paper, the effective ℇs is calculated numerically using the PC software EXCEL by drawing the electrical fluxes and analyzing the effect of the insulator for each flux. The calculation result for VVF cable considering the limited insulator area around the conductors shows that the effective ℇs is about 13% less and the transmission speed is 7% faster than when the insulator occupies the full space around the cable. © 2009 Wiley Periodicals, Inc. Electr Eng Jpn, 167(4): 24–31, 2009; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/eej.20862 [ABSTRACT FROM AUTHOR]

A severe fault may cause loss of synchronism of a small number of generators. And it may take many generators out of service resulting in a wide area blackout. When two groups of generators lose synchronism, the magnitude of voltage on some lines becomes zero. Therefore, an approach whereby lines with zero voltage are opened has been employed in order to prevent loss of synchronism from extension. This paper presents a new method using voltage and current measured on a line during disturbance to detect the line with zero voltage at the instant when loss of synchronism takes place. A method to detect loss of synchronism using voltage and current measured on a line was already proposed. This paper presents results of the tests performed using a power system simulator which is composed of a DC motor, a synchronous generator, artificial transmission line, circuit breaker equipment, and so on. The validity of the proposed methods was verified by finding loss of synchronism correctly. © 2006 Wiley Periodicals, Inc. Electr Eng Jpn, 155(4): 7–19, 2006; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/eej.20346 [ABSTRACT FROM AUTHOR]

The authors have proposed FRIENDS—Flexible, Reliable and Intelligent Electrical eNergy Delivery System—as a future electric power distribution system. The most important idea of FRIENDS is to install new facilities called Quality Control Centers (QCCs) between the distribution substation and customers. By controlling QCCs appropriately, various purposes of FRIENDS can be achieved. It is indispensable to design the concrete interior structure of QCC in order to realize FRIENDS. This paper proposes the interior structure and control methods of QCC from the viewpoint of power conditioning functions by energy storage system in QCC. In this paper, it is assumed that SMES is used as the energy storage system in QCC. The proposed interior structure is based on the concept of UPS (Uninterruptable Power Supply). In this paper, SMES is installed in the DC side of UPS. Further, this paper proposes control methods of SMES and PWM converters. The proposed control methods are used to satisfy various purposes, such as load fluctuation compensation, load leveling, and cooperation with dispersed-type generator. Finally, the validity of these control methods is confirmed through transient analysis PSCAD/EMTDC. © 2003 Wiley Periodicals, Inc. Electr Eng Jpn, 143(3): 20–28, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/eej.10056 [ABSTRACT FROM AUTHOR]

Researches on the unit commitment with transmission network have been reported recently. However, most of these researches mainly discussed the security constrained unit commitment, while the relationship between unit commitment and transmission losses was not considered. However, from the standpoint of operating reserve for ensuring power supply reliability, a unit commitment considering transmission losses is required. Further, under the deregulation and liberalization of the electric power industry, not only the line's security but also transmission losses are expected to play an important role in calculating the network access charge, and unit commitment taking into account transmission losses is also desired from this viewpoint. In this paper, a unit commitment approach with both transmission losses and line flow constraint is presented. Based on a heuristic iterative optimization method, first, an initial schedule is created by using a successively decommitting unit approach that is proposed in this paper. Then, we determine constraints included in the unit commitment schedule by a heuristic iterative optimization approach, in which an algorithm able to get rid of line overload by DC optimal power flow is developed. Through numerical simulations on two test power systems, the effectiveness of the proposed method is shown. © 2003 Wiley Periodicals, Inc. Electr Eng Jpn, 142(4): 9–19, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/eej.10116 [ABSTRACT FROM AUTHOR]

SUMMARY This paper discusses nontheoretical harmonics on the dc-side of a 12-pulse rectifier in dc railway systems. These harmonics are the commercial frequency component and the doubled component. The causes of these harmonics are (a) diode forward voltage drop difference, (b) transformer secondary inductance difference, (c) voltage harmonics at the ac-side of the rectifier, and (d) effects of the voltage induced by adjacent high-voltage power transmission lines. We evaluated cases (a), (b), and (c), as case (d) has been previously studied . The results of the evaluation were as follows: · The effects of both the transformer secondary inductance difference and the voltage harmonics inside the electric power system are not negligible in some cases in the discussion of the EMC problem among railway equipments. · If there are several traction circuits in parallel, each of which consists of an input filter, an inverter, and several traction motors, the harmonic reduction effect of the filters weakens significantly. [ABSTRACT FROM AUTHOR]

For transmission-line surge studies, the inclusion of corona discharge due to high voltage surges is important as well as the inclusion of frequency-dependent effects. Because the charge-voltage (q-v) curve of a lightning surge is different from that of a switching surge, a corona model should reproduce different q-v curves for different wave-front times. The present paper proposes a wave-front time dependent corona model which can express the dependence by a simple calculation procedure as accurately as a rigorous finite-difference method which requires an enormous calculation time. The simplicity enhances the incorporation of the corona model into a line model, because a large number of models are to be inserted into the line model by discretization. The q-v curves calculated by the proposed method agrees well with field tests. This paper also proposes an efficient method to deal with nonlinear corona branches in distributed-parameter line model using the trapezoidal rule of integration and the predictor-corrector method. © 1999 Scripta Technica, Electr Eng Jpn, 129(1): 29–38, 1999 [ABSTRACT FROM AUTHOR]

Various countermeasures are taken against lightning faults in power transmission lines to decrease their occurrence and improve transmission reliability. However, how much they enhance the power transfer capability has not yet been quantitatively evaluated. The conventional deterministic approach, which is widely used in power system planning methodology, is inadequate to deal with this issue. This paper proposes a new method for numerically defining the power transfer capability enhanced by countermeasures against lightning. The proposed method is based on a probabilistic approach in which several fault patterns are taken into consideration with their occurrence frequency and maximum transferable power. This paper also gives an example application of the proposed method to a model trunk transmission system. The effect of a third overhead ground wire on the increase of transfer capability of a 500 kV transmission line has been quantitatively evaluated. [ABSTRACT FROM AUTHOR]

This paper describes a new approach to the analysis of the back-swing phenomena in multimachine power systems. When a short-circuit fault occurs in a power system, some generators decelerate in a short period immediately after the fault in some cases. The phenomenon called back swing is caused by the transient responses in armature winding of synchronous machines and in transmission lines. To represent the back swing in detail by a mathematical model, these transient behaviors have to be described by sets of differential equations. Then not only does the order of differential equations increase, but the convenient expression of the transmission system by a set of node equations becomes useless. In this paper an equivalent power system model for the simple representation of the back swing has been proposed. First, an impedance for each machine that represents the transient of transmission system has been introduced. It is assembled into the differential equations associated with armature winding response. Then the transmission system is represented by a constant impedance matrix. This model makes it possible to calculate the transient behavior of armature flux in multimachine power systems. The transient torque brought to the rotor shaft by the flux is calculated directly and it represents the back-swing phenomena effectively. [ABSTRACT FROM AUTHOR]

The authors have investigated the operational feasibility of a future metropolitan electric power system associated with highly densified cryogenic cables. A new concept of power system configuration with cryogenic cables and its operation have been proposed. Three different models of future power transmission systems in large cities of Japan have been constructed as the background systems prior to introduction of cryogenic cables in the 21st century. This paper considers one of the three models which is characterized by its conventional transmission system constructed mainly by 154-kV transmission lines stepping don directly from the 500-kV outer ring without any intermediate voltage class. This paper also discusses whether or not the power system model will be operated effectively together with cryogenic cables to supply demands forecasted in the period subsequent to the first decade of the 21st century. The computer simulations are carried out to obtain power flow and bus voltage distributions for a peak load period as well as for an off-peak one in the power system model. These simulations reveal that the conventional background power system should be arranged very carefully before introducing the cryogenic cables to facilitate their operations. (1) On a contingent trip of a cryogenic cable in the peak in the peak load period, not all bus voltages are expected to be kept within a tolerant zone due to the high impedance of 154-kV conventional transmission lines in the power system model. (2) Thus it is proposed that the background conventional system prior to introduction of cryogenic cables should be developed not only by extension of 154-kV conventional transmission lines but also by introduction of 275-kV lines. (3) Bus voltage rises induced in the off-peak load period are reduced by effective utilization of 275-kV conventional transmission lines. [ABSTRACT FROM AUTHOR]

This paper discusses the features of tie-line flow fluctuation for dynamic security assessment by monitoring the system response and detecting the transition trend from the normal to the alert state. The spectrum analysis of the field data which have been acquired at the IWAKI line between Tohoku Electric Power Co. and Tokyo Electric Power Co., shows that a small fluctuation is always observed in the line-power flow with an intrinsic oscillatory mode. The undamped oscillation of the intrinsic mode occurs when the operating condition is close to the alert state. In this paper, the relation between the spectrum indices and the generating allocation is discussed by numerical investigation of the field data to construct the knowledge database for dynamic security assessment. Also, it is shown that the transition of the system state can be evaluated by continuously monitoring the line-flow fluctuation spectrum. The spectrum domain partitioning to evaluate the power flow fluctuation quantitatively is proposed. Effects of generating allocation into the power spectrum are studied statistically. Model analysis is also done to explain the relation of the field data. The obtained results are reasonable compared with the experience of the power system engineer, and useful for the advancement of the security assessment. [ABSTRACT FROM AUTHOR]

SUMMARY In this paper, representations of a perfectly conducting thin wire and an imperfectly conducting medium in the transmission line modeling (TLM) calculation are briefly explained. Then, the method is applied to analyzing surge responses of a vertical parallelepiped grounding electrode and a square-loop grounding electrode. Surge responses calculated using the TLM method agree reasonably well with the corresponding responses measured and calculated using the finite-difference time-domain method. It is probably the first time that surge responses of grounding electrodes have been analyzed reasonably accurately using the TLM method. [ABSTRACT FROM AUTHOR]

SUMMARY The prospective transient recovery voltage (TRV) at current interruption for circuit breakers should be measured by using an ideal circuit breaker. Prospective values of the TRV are obtained by drawing the tangential line to the TRV waveform. But, it is difficult to draw the tangential line on the 4-parameter TRV waveform automatically by computer software. This paper presents a new method of drawing the tangential line on the 4-parameter TRV waveform. It is easy to draw the tangential line on the TRV waveform by a simple waveform transform process. This method is easy to code as computer software. We also investigate the method of deciding the current zero in prospective TRV measurements. [ABSTRACT FROM AUTHOR]

SUMMARY This paper evaluates the optimal power generation mix considering massive deployment of variable renewable energy and regional power interchange. Japan has initiated the feed-in-tariff (FIT) and expected the significant introduction of PV and wind power for energy self-sufficiency and climate change. However, wind power resources in Japan are concentrated mainly in Hokkaido and the Tohoku region, which are remote from electricity-consuming areas such as Tokyo, and facilitating the considerable deployment of wind power requires the establishment of inter-regional power transmission lines. Against these backgrounds, we develop an optimal power generation mix model including regional electricity exchange as a large-scale linear programming model with 10 million variables and 30 million constraints. The calculation results show that regional grid expansion encourages wind power installation in the Hokkaido and Tohoku regions for power supply to the Tokyo area, where PV power and stationary batteries are alternatively replaced. Grid expansion too promotes the shift of PV installation to the Kyushu and Shikoku regions, which have longer sunshine duration, and interchangeably mitigates PV deployment in other regions through the transport of PV power from those two regions. [ABSTRACT FROM AUTHOR]

In Japan, the grounding resistance of surge arresters (Arrs) for the lightning protection of power distribution lines is generally maintained below 30 Ω. Therefore, electric power companies have been spending large amounts of money on the construction and maintenance of low grounding resistances. In this paper, the influence of grounding resistance on lightning protection measures for power distribution lines with both a ground wire (GW) and Arrs is investigated by EMTP analysis and experiments. These results showed that even if the grounding resistance of Arrs becomes high, the effectiveness of lightning protection is hardly decreased. The results also indicated that it is more important for constructing a rational lightning protection system to install a large number of lightning protection devices on power distribution lines than to lower the grounding resistance of Arrs. © 2012 Wiley Periodicals, Inc. Electr Eng Jpn, 179(3): 10-22, 2012; Published online in Wiley Online Library (). DOI 10.1002/eej.21280 [ABSTRACT FROM AUTHOR]

The problem of recovery from power-system failures is the problem of handling operations that make it possible to supply power from other lines in response to power-system failures or construction by switching between the opened and closed states of sectionalizing switches. Considerable research has already been conducted with regard to this issue. This paper addresses the issue of determining target systems for final recovery in cases when some sections remain subject to power failure (i.e., sound bank capacity < load capacity). For this purpose, intersection is conducted only for parameters within such power-failure sections. In such research, calculations are implemented by setting a value of 2 to the sectionalizing switches of a single parameter. In addition, when the state of a sound section changes due to mutation improvements, the method of simultaneously changing the selected points and neighboring sectionalizing switches is applied. It is clear that the proposed method, consisting of conventional GA only, is superior in terms of average fitness values. © 2011 Wiley Periodicals, Inc. Electr Eng Jpn, 176(1): 9-17, 2011; Published online in Wiley Online Library (). DOI 10.1002/eej.21092 [ABSTRACT FROM AUTHOR]

It is very important to maintain supply reliability in the deregulated environment. The transient stability problem is one of the major concerns in studies of planning and operation of power systems. Time domain simulation is currently the best available tool for allowing the use of detailed models and for providing reliable results. The main limitations of this approach involve long computation times. Therefore, this paper proposes a transient stability evaluation method using minimum transient kinetic energy of postfault trajectories. This method can estimate critical clearing times with only two points of the minimum transient kinetic energy, regardless of whether the trajectories after the clearing time are stable or unstable. The validity of the proposed method is shown by simulation studies with the IEEJ EAST 10-machine 47-bus system. © 2010 Wiley Periodicals, Inc. Electr Eng Jpn, 174(3): 18-24, 2011; Published online in Wiley Online Library (). DOI 10.1002/eej.21018 [ABSTRACT FROM AUTHOR]

In a low-voltage distribution line in a three-phase four-wire system, the neutral conductor current is increased by a current consisting mainly of the third harmonic, which has no phase rotation if the balance of the load has been removed, when harmonic generation equipment is included in the load. The increase of this neutral conductor current increases the waveform distortion of the receiving end voltage, and various kinds of waveform interference occur. To reduce the neutral conductor current, insertion of an active filter for the third harmonic wave near the load has been proposed, and a protective effect against waveform interference has also been reported. In this paper, a method for drastically reducing the neutral conductor current by using LC resonance, which is simpler than an active filter, is proposed. © 2010 Wiley Periodicals, Inc. Electr Eng Jpn, 171(4): 19–27, 2010; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/eej.20897 [ABSTRACT FROM AUTHOR]

The theories of operation of existing relays are roughly divided into two types: the current differential type based on Kirchhoff's first law and the impedance type based on Kirchhoff's second law. We can use Kirchhoff's laws to rigorously formulate fault phenomena, so the circuit equations are represented as nonlinear simultaneous equations whose variables are the fault point k and the fault resistance Rf. This method has two defects: (1) a heavy computational burden in iterative calculation by the N-R method and (2) the relay operator cannot easily understand the principle of numerical matrix operation. The new protection relay principles proposed in this paper focus on the fact that the reactance component at the fault point is close to zero. The reactances Xf(S) and Xf(R) at the ends of the branch are calculated by solution of linear equations. If the signs of Xf(S) and Xf(R) are not the same, it can be inferred that the fault point is located in the branch. This reactance Xf corresponds to the difference in branch reactance between the actual fault point and an imaginary fault point. Thus, the relay engineer can understand the fault location in terms of the concept of “distance.” Simulation results using this new method indicate that it can provide much more precise estimation of fault locations than those obtained by inspection of operating transmission lines. © 2009 Wiley Periodicals, Inc. Electr Eng Jpn, 168(1): 29–40, 2009; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/eej.20720 [ABSTRACT FROM AUTHOR]

Crosstalk is induced by a reflected wave of a load connected with a transmission line. Thus, analysis of the reflected wave is important. The reflected wave generated from a nonlinear load is complicated. In order to estimate the complicated reflected wave, we measured the reflected and incident waves for the nonlinear load and estimated the dynamic C-V characteristic, which explains the relation between the incident and reflected waves. This paper reports a simple experimental method of extracting reflected waves at a varactor load and presents estimates of the dynamic C-V characteristic of the load. It is shown that the reflected voltage waves simulated using the dynamic C-V characteristic agree with the measured results. © 2009 Wiley Periodicals, Inc. Electr Eng Jpn, 167(4): 32–38, 2009; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/eej.20821 [ABSTRACT FROM AUTHOR]

Most general-purpose analyzers for harmonic analysis on distribution lines are designed to sample the data of one or two power supply periods. In other words, these analyzers process waveforms and display the results based on the assumption that the analyzed waveforms contain no noninteger components, such as subharmonics and interharmonics. When waveforms containing noninteger components are analyzed with these general-purpose analyzers, the results often indicate components that are not actually present. This paper proposes a technique of waveform judgment and explains its method of application. The technique allows noninteger components to be recognized in analyzed waveforms from the properties of Lissajous figures, and clarifies the types of components and the time windows necessary for appropriate analysis. © 2008 Wiley Periodicals, Inc. Electr Eng Jpn, 166(2): 32– 38, 2009; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/eej.20536 [ABSTRACT FROM AUTHOR]

This paper investigates induced voltage characteristics from an overhead transmission line by applying a method of modeling of induced voltages proposed by the authors. EMTP simulation results obtained by the modeling method agree with analytical results obtained from a well-known formula. The induced voltages are significantly dependent on the configuration of the overhead line. A horizontal line induces the largest voltage in a gas pipeline, and the voltage induced by a vertical twin-circuit line is about 20% smaller than that induced by a vertical single-circuit line. The method is applied to a real pipeline system and the simulation results show reasonable agreement with field test results. © 2008 Wiley Periodicals, Inc. Electr Eng Jpn, 164(1): 43–51, 2008; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/eej.20465 [ABSTRACT FROM AUTHOR]

Corona discharge may cause audible noise, and it is frequently generated from wet conductors of high-voltage AC overhead transmission lines. Audible noise arises more easily from new conductors that have lubricating oil on their surface than from aged conductors. In this paper, the corona characteristics, particularly the audible noise, of conductors having various wetting properties are presented for the purpose of developing a corona-free conductor for AC overhead transmission lines. It was found that a conductor having a super-hydrophobic surface exhibited a minimized audible noise level, but it does not have sufficient durability for practical applications. Furthermore, a conductor having a super-hydrophilic surface made by thermal spraying of TiO2 showed good performance regarding the suppression of audible noise. The thermal spraying of TiO2 seems to be an effective processing technique that has sufficient durability for practical applications. © 2007 Wiley Periodicals, Inc. Electr Eng Jpn, 159(3): 19–25, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/eej.20509 [ABSTRACT FROM AUTHOR]

In long distribution systems, Step Voltage Regulators (SVRs) are installed to regulate the system voltage. There are some papers on finding optimal placements of SVRs in the system. However, there is no analytic method that focuses on the voltage margin, that is, the optimal placement with respect to the system voltage. The authors propose a method of finding the placement of an SVR so that the voltage margin from the upper (or lower) voltage limit is the largest under heavy load. In order to deal with sets of loads that are dispersed over the entire distribution line, we derive the differential equation of the complex power and that of the voltage drop, which are expressed as functions of distance from a substation. The voltage profile is obtained as a cubic equation by solving the voltage equation if the load distribution is trapezoidal. The method of finding the optimal SVR placement distinguishes three modes with three different voltage profiles. One is the case in which the transformation ratio of the SVR is small and the system length is short, one is the case in which the transformation ratio of the SVR is large and the system length is short, and the third is the case in which the transformation ratio of the SVR is large and the system length is long. The optimal placement and tap position of the SVR are calculated by solving the above-mentioned equations in these three modes. It is confirmed that the proposed analytical method is appropriate by model calculation results. © 2007 Wiley Periodicals, Inc. Electr Eng Jpn, 158(4): 11–21, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/eej.20481 [ABSTRACT FROM AUTHOR]

Although power-line communications are expected as a promising method to realize an in-home network, one of their difficulties is an unnecessary radiation due to the electrical unbalance of power-line channels. To solve the problem, the statistical data of electrical unbalance based on measurements in the practical fields, that is, many and various Japanese residential power lines, must be collected as the first step. In this paper, a method to produce a longitudinal-conversion-loss (LCL) probe that can be used for the practical measurement is studied. The LCL is a measure of the electrical unbalance, and is often used to determine the impairment of EMC performance of a system by the cabling. To improve the dynamic range of the probe, an adjustment method of the transformers' parameters is proposed. According to our scenario, the obtained dynamic range was better than that of the conventional probe with the frequency band higher than 2 MHz. The achieved improvement was 6 dB at 6 MHz, and 14 dB at 30 MHz, for example. © 2006 Wiley Periodicals, Inc. Electr Eng Jpn, 155(3): 38–44, 2006; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/eej.20166 [ABSTRACT FROM AUTHOR]

This paper describes a control scheme of fault current limiter by series voltage injection. The current limiter proposed in this study is based on the use of a SMES-based series-connected voltage sag compensator, which has been previously studied by the authors, for controlling fault current caused by short circuit on the load side. An algorithm for fast discriminating between power system voltage sag and load-side short circuit is proposed for the equipment to correctly function either for voltage sag compensation or for fault current limiting purpose. Furthermore, a new control strategy based on output voltage phase control of the series compensator is proposed for current limiting with good waveform characteristics and low active power absorption. Experimental results demonstrated the validity of the proposed strategy. © 2006 Wiley Periodicals, Inc. Electr Eng Jpn, 155(2): 64–72, 2006; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/eej.20128 [ABSTRACT FROM AUTHOR]

Open access to electric power transmission networks has been carried out in order to foster generation competition and customer choice worldwide. When several PPSs request to simultaneously supply power to customers based on bilateral contracts, it is expected that the transmission network accepts amounts of wheeled power requested by the PPSs as much as possible. It is possible to maximize total requested wheeled power by controlling power flow through transmission lines. It is well known that FACTS device is available to control line flow flexibly. In this paper, in order to maximize total wheeled power simultaneously requested by several PPSs, the authors propose an algorithm to determine the optimal reactance of TCSC (a type of FACTS device). The proposed algorithm is based on Particle Swarm Optimization (PSO), which is an optimization method based on swarm intelligence. In the proposed algorithm, PSO is improved to enhance ability of searching global minimum by giving different characteristic to behavior of each agent. In order to check the validity of the proposed method, numerical results are shown for 6 and IEEE 30 bus system models. © 2006 Wiley Periodicals, Inc. Electr Eng Jpn, 155(2): 17–26, 2006; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/eej.20085 [ABSTRACT FROM AUTHOR]

We have developed a digital real-time simulator of Power Electronics Controllers, so-called FACTS (Flexible AC Transmission Systems) Controllers and/or Custom Power by using MATLABTM/SIMULINKTM and dSPACETM System. This paper describes the modeling and the calculation accuracy of a UPFC (Unified Power Flow Controller) model. Hence, the developed simulator operates at a large time step, in order to improve simulation accuracy, a correction processing of the switching delay is implemented into the UPFC model. Calculation accuracy of the real-time UPFC model is at the same level as EMTDCTM results. We confirm stable operation of the developed UPFC model by connecting a commercial real-time digital simulator (RTDSTM). © 2006 Wiley Periodicals, Inc. Electr Eng Jpn, 155(1): 19–26, 2006; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/eej.20200 [ABSTRACT FROM AUTHOR]

This paper describes the effect of mutual leakage reactance in the rotor circuit on the analysis of generator transient characteristics. The authors derive a detailed equivalent circuit model for a 48P-15,750-kVA generator, analyze sudden short circuits and asynchronization phenomena of the generator by simulations with an electromagnetic transients program (ATP-EMTP), and compare the results with experimental data. © 2005 Wiley Periodicals, Inc. Electr Eng Jpn, 153(3): 31–40, 2005; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/eej.20147 [ABSTRACT FROM AUTHOR]

In gas-insulated switchgear (GIS), the arc discharge due to a disconnector on/off generates fast transient surges, which can be the cause of malfunction and damage to electronic devices such as microprocessors and AD converters, if the fast transient surge exceeds a specified level. In this paper, it is shown that the comparison and evaluation are realized between the measured results and the calculated ones of fast transient surges generated due to a disconnector on/off in 300 kV GIS by adopting the evaluation index. The calculation is carried out by applying the authors' proposed equivalent circuits using distributed constant lines in consideration of the structure of GIS and a newly developed divided-type voltage sensor. Also, it is found by using the evaluation index that the measured results and the calculated results are in good agreement with each other. Furthermore, the cause of the occurrence of the peak of the evaluation index is clarified by analyzing the equivalent circuit. And the signal conditioning using a low-pass filter for electronics circuits connecting the divided-type voltage sensor is designed. © 2004 Wiley Periodicals, Inc. Electr Eng Jpn, 149(2): 34–42, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/eej.10360 [ABSTRACT FROM AUTHOR]

This paper proposes a high-speed reclosing operating method to improve the stability in a power system. The proposed method calculates the reclosing time, taking a standard case in which the reclosing is not done using the generator phase angle δ, and the angular velocity ω, and the field system voltage ed'. Also, the execution of reclosing time is calculated, while taking into consideration the acceleration/deceleration energy of the generator during a fault. It can be expected that δ is suppressed by this optimum reclosing operation. Therefore, the system stability can be expected to improve by carrying out high-speed reclosing when a fault occurs. At present, it has been set at a value which seems to be optimal considering various problems in the reclosing time. However, in those methods, the system stability improvement effect cannot be expected. It was demonstrated that the high-speed reclosing method serves to depress δ in the computer simulation. [ABSTRACT FROM AUTHOR]

This paper investigates the surge propagation characteristics of an 1100- kV transmission line based on field test results and EMTP simulations. The EMTP simulations shows that the arc horn voltage is almost the same as the phase-wire voltage to earth, and thus the measured arc horn voltage can be regarded as the phase-to-earth voltage. The surge-wave deformation after a distance greater than 2 km measured in the field test is analytically explained as due to separation of modal traveling waves, the earth-return and the aerial modes, because the travel times of the two modes become noticeably different. A distinctive feature of the 1100-kV line is its very small attenuation, about half that on a 500-kV transmission line. [ABSTRACT FROM AUTHOR]

Recently, the electric utility industry worldwide has been facing pressure to be deregulated or restructured in order to increase its efficiency, to reduce operational cost, or to give consumers more alternatives. For this aspect, a great deal more research is needed to achieve a better, intelligent knowledge process. The present centralized system for power system control, operation, and planning must be remodeled to cope with these situations. With the promotion for the deregulation of the electric power system, the definition of the objective function for the optimization problem such as outage work operation for electric power systems is becoming critical. Currently, agents are an intense focus in many subfields of computer science and artificial intelligence. Agents are being used in an increasingly wide variety of applications. In this paper, we developed a power system normal operation application by multiagent architecture. Our multiagent system consists of several facilitator agents, equipment agents, and switch-box agents. Facilitator agent acts as a manager for negotiation process between agents. Equipment agent corresponds to the element of the electric power system, such as bus, transformer, and transmission line, while switch-box agent is the pseudo object which consists of neighboring current breakers and disconnecting switches. The proposed system realizes the appropriate switching operations by interacting with corresponding agents. The proposed approach is applied to a simple network, and the results show that the proposed multiagent system is an efficient decentralized approach for solving power system normal operations. © 2004 Wiley Periodicals, Inc. Electr Eng Jpn, 146(4): 26–33, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/eej.10227 [ABSTRACT FROM AUTHOR]

In Japan, local power systems (77 kV) are served from the 275- or 154-kV substations. For enhancement of power supply reliability, the transmission lines are connected to several substations, and the operational configuration is radial. The local power system's configuration is determined by connecting and disconnecting transmission lines so as to keep the radial structure and satisfy the operation constraints. When a local power system has a number of transmission lines, many configuration candidates occur. Recently, an IEEJ committee made a practical scale local system model (IEEJ Local System Model). Since the IEEJ Local System Model has 76 transmission lines, the total number of configuration candidates is 276 (approximately 7.5 × 1022). In this paper, the authors try to strictly obtain the loss-minimum configuration under constraints such as substation capacity, line capacity, and radial structure in the IEEJ Local System Model. In order to obtain the optimal configuration, a new computation algorithm is proposed. In the proposed algorithm, the configuration determination problem is replaced as two combinatorial optimization problems based on the operational constraints [(1) substation capacity, (2) line capacity, and (3) radial structure]. One combinatorial optimization problem (subproblem 1) is to pick up all partial configurations so as to minimize total line loss under the substation capacity constraint. By using the enumeration method, subproblem 1 is solved. Subproblem 2 is solved by using the reduced ordered binary decision diagram (ROBDD). Since the proposed method is based on enumeration and Boolean function, the optimality of obtained solution is guaranteed. © 2004 Wiley Periodicals, Inc. Electr Eng Jpn, 146(4): 34–42, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/eej.10226 [ABSTRACT FROM AUTHOR]

This paper describes the outline and results of the lightning impulse tests for a 275-kV full GIS substation. The behavior of lightning surges is a very important factor for the rational design of substations and low-voltage and control circuits inside the substations. For the above reason, we carried out lightning impulse tests for a new 275-kV full GIS substation. In these tests, we measured voltage induced in low-voltage and control circuits, transient characteristics of grounding grid, injected voltage and current waveforms, and so on. By investigating these data, we confirmed the behavior of lightning surges inside the substation. We also compared simulated waveforms by EMTP analysis with the measured waveforms. The simulated results agreed well with the measured results. © 2003 Wiley Periodicals, Inc. Electr Eng Jpn, 146(1): 46–58, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/eej.10230 [ABSTRACT FROM AUTHOR]

Because of the introduction of deregulation and competition in the electricity supply industry, large numbers of IPPs (Independent Power Producers) will get into the market. It has become much more important to be able to determine which generators are supplying a particular load, which generator is responsible for transmission line congestion, and what is each generator's contribution to the system losses. In this paper, we propose a way to calculate these contributions automatically. The applicability of the proposed technique is demonstrated using the EAST 10 47-bus power system. © 2003 Wiley Periodicals, Inc. Electr Eng Jpn, 144(3): 28–35, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/eej.10181 [ABSTRACT FROM AUTHOR]

This paper presents the fundamental surge phenomenon when a step voltage is applied to a horizontal line above the ground which has branch feeders. We study line current and voltage at joint with the method of moments that calculates electromagnetic field in frequency domain. It is widely noted that the current reflection factor changes to a third at the junction of the same three lines in conventional transmission line theory based on TEM wave, and the stepwise current reflected appears overlapping to the incident current. On the other hand, the reflected current from the joint shows the inductive characteristic or the capacitive one depending on the angle between lines, which varies gradually and not stepwise in our numerical analysis considering TM wave. The time characteristic of the voltage at joint depends on the angles also, and the peak voltage slightly exceeds the voltage by the transmission line theory. These phenomena are caused by the electromagnetic coupling between the main line and branch lines. In addition to the computer simulations, we measured the currents in the reduced-scale model lines and the results show the validity of our analysis regarding changes of the reflected current depending on the angles. © 2003 Wiley Periodicals, Inc. Electr Eng Jpn, 144(2): 1–8, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/eej.10176 [ABSTRACT FROM AUTHOR]